This composite image from the Chandra X-ray Observatory shows two tails of X-ray emission in galaxy cluster Abell 3627.

At the front of the tail is the galaxy ESO 137-001. The brighter of the two tails is about 260,000 light years long. It has been seen before, but scientists were surprised to see the second, fainter tail.

The X-ray tails were created when cool gas from ESO 137-001 (with a temperature of about 10°K) was stripped by hot gas (about 100 million degrees) as it travels towards the centre of the galaxy cluster Abell 3627. What astronomers observe with Chandra is essentially the evaporation of the cold gas, which glows at a temperature of about 10 million degrees. Evidence of gas with temperatures between 100 and 1,000°K in the tail was also found with the Spitzer Space Telescope. Galaxy clusters are collections of hundreds or even thousands of galaxies held together by gravity that are enveloped in hot gas. The two-pronged tail in this system may have formed because gas has been stripped from the two major spiral arms in ESO 137-001. The stripping of gas is thought to have a significant effect on galaxy evolution, removing cold gas from the galaxy, shutting down the formation of new stars in the galaxy, and changing the appearance of inner spiral arms and bulges because of the effects of star formation.

The composite image shows X-rays from Chandra in blue, optical emission in yellow and emission from hydrogen light (H-alpha) in red. The optical and H-alpha data were obtained with the Southern Astrophysical Research (SOAR) Telescope in Chile.